Envelope processing systems, such as mail piece processing, sorting and bar code application systems, typically include an envelope stacking apparatus at the end of the system to secure the sorted mail pieces in a stacked position to facilitate orderly removal of the processed mail pieces from the system. The stacked mail pieces are manually or automatically removed from the stack and/or bound by an operator.
One such stacking apparatus is disclosed in U.S. Pat. No. 4,955,596, commonly assigned. An envelope to be stacked, or any suitable sheet-like article, is forcibly fed on edge into a discharge magazine where it is stacked in a somewhat compressed array with other, previously fed envelopes. The envelope enters the discharge magazine via a dual stacker belt transport configuration, wherein a pair vertically juxtaposed stacker belts rotate about rollers disposed in a triangular array. The rollers each are rotatably mounted on shafts having a fixed axis.
The discharge magazine includes multiple transport belts that may have smooth surfaces, or may have track-like protrusions extending above the discharge magazine floor to engage the bottom edges of the stacked envelopes and advance the envelopes away from the stacker belts to permit the free entry of additional envelopes into the stacker region. The transport belts are activated by a stack sensor mechanism that includes a spring biased, pivotally mounted lever arm which extends through a gap between the pair of stacker belts. The tip of the lever arm contacts the last envelope to enter the stack. As the stack gets larger and the laterally applied normal force of the stacked envelopes overcomes the bias of the lever arm spring of the sensor mechanism, the lever arm trips a switch that in turn activates a drive motor connected to the transport belts to move the envelopes away from the stacker belts. This reduces the normal force or pressure exerted by the stack of envelopes on the stacker belts, and provides space for the entry of subsequent envelopes into the stack.
Although the stack sensor lever arm in the prior art apparatus contacts the last envelope in the stack, the lever arm contacts the last stacked envelope over a small plane, or sometimes a point, and is therefore highly susceptible to planar and height variations associated with the last stacked envelope. In high speed mail processing systems, a problem arises when the last envelope in the stack tilts such that the bottom edge and the top edge of the envelope no longer form a substantially vertical plane. As the stack becomes increasingly tight, accurate pressure sensing is critical to avoid jamming. Jamming occurs as a consequence of erroneous stack pressure sensing, when a tilted edge of the last stacked envelope obstructs the entrance to the stack of the next envelope to be stacked. Such problems are compounded when the stacker is used for simultaneously stacking a plurality of different sized (varying in height and thickness) envelopes.
Erroneous stack pressure sensing typically occurs where the lever arm contacts the tilted envelope at a surface or point that is tilted furthest away from the stacker belts. This surface exerts less force on the lever arm than the surface closest to the stacker belt. The lever arm's small plane or point of contact may erroneously indicate that the stack can receive more envelopes when the stack is actually too tight to properly receive another envelope without first activating the transport belts.
In view of the foregoing, an object of the present invention is to provide a high speed stacking apparatus and method that accurately senses the stack pressure of tilted articles to substantially reduce the occurrence of article jamming.
Another object of the present invention is to provide an apparatus and method that automatically and accurately senses the pressure applied by a stacked group of processed envelopes on a stacker conveying mechanism regardless of the degree of tilt of the last envelope to enter the stack, and in response thereto generates a signal to actuate an envelope transport system for advancing the documents in the stack away from the stacker conveyor means, thereby relieving the pressure on the conveying mechanism and creating space for the facile entry of additional processed envelopes into the stack.
A further object of the present invention is the provision of a sensor apparatus for a conveying belt mechanism for an envelope stacker device whereby one of the roller elements supporting the belt mechanism is on a laterally displaceable axis, whereby the axial displacement of the roller element is responsive to the force applied to the sensor apparatus by the stack of envelopes regardless of the angle of vertical orientation of the envelopes in the stack as the envelopes engage the sensor apparatus.
Yet another object of the present invention is the provision of an automatically actuated kicker mechanism that senses the trailing edge of an envelope entering the stack, and kicks the trailing edge away from the conveyor belts and onto an auger which drives the envelope's tracking edge outward to cooperate with the stack pressure sensor and control device to ensure that space is provided in the stack to permit subsequent envelopes to be fed into the stack without jamming.